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Results for “Neuromuscular adaptability”

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At least 217 records · Page 12Linked to original sources

PubMed1997

Changes in knee joint function over a wide range of walking speeds.

OBJECTIVE: Changes in patterns of knee joint flexion-extension rotations, moments and powers were investigated during the stance phase across a wide range of walking speeds that includes the very slow speeds used by many patients referred for gait analysis. DESIGN: Each subject walked at 25, 50, 75, 100, and 125% of a scaled natural speed of 0.785 statures.s(-1). BACKGROUND: The results of earlier studies suggest that control subjects, as they walk at progressively slower speeds, increasingly use a large internal knee flexor moment in the early stance phase. METHODS: Eighteen healthy adult subjects (nine male and nine female) were tested. RESULTS: The shapes of the mean patterns were similar for the three fastest, most natural walking speeds. At the two slowest speeds, however, subjects used little knee flexion and small knee moments through mid-stance, resulting in negligible joint power through the first 80% of the stance phase. At these speeds, most subjects had moment patterns that could not be classified with confidence as 'normal' or as predominantly flexor or extensor. Only four subjects had knee flexor moment patterns at the slowest speeds, and these included much smaller flexor moments in the early stance phase than in some previous reports. RELEVANCE: Many patients walk at very slow speeds for which 'normal' joint kinetic patterns have not been described. The knee joint kinetic data provided here from healthy subjects is useful in helping to distinguish 'abnormal' patterns caused by neuromuscular pathologies or adaptations from patterns reflecting the effects of slow walking speed alone.

Journal Article↗

PubMed1997

The influence of different floor stiffness on mechanical efficiency of leg extensor muscle.

The mechanical behaviour of skeletal muscle is influenced by internal factors (e.g. re-use of elastic energy) and/or external conditions (e.g. floor compliance, shoe structure etc.). These factors have an effect on muscular work economy-this was investigated in the present study. Eight subjects were tested during three different series of jumps. Each series consisted of rhythmical vertical jumps performed at desired frequency and height for 1 min. The first (1) series was executed on the laboratory floor without rebound condition (subjects were asked to maintain 1 s period in an isometric condition before concentric work was performed), the second (II) and the third (III) series were performed in rebound conditions respectively on a laboratory floor (hard surface) and on a special panel possessing high compliance (a special foam rubber panel with stiffness of 14.4 kN/m). Expired air was collected during the test and recovery for determination of energy expenditure. Mechanical work was calculated from the vertical displacement of the body during the jumps. The results indicated that the net efficiency in the jumps without prestretch of the leg extensor muscles (series I) was the lowest (19.4%). In contrast, the net efficiency observed in rebound jumps (series II and III) was respectively 30.8% and 33.1%, demonstrating that the reuse of elastic energy (Wel) plays an important role for muscular work efficiency. However, the contribution of Wel to the total work performed was different p < 0.05, Student's t-test) in jumps on the special panel (41%) compared to the normal surface (37%), even if the total amount of stored elastic energy was the same in both conditions. The different efficiency observed between series II and III was attributed to the compliance of the surface on which the tests were executed. It was suggested that man could change his neuromuscular pattern to adapt muscular behaviour for matching the damped properties shown by the high compliance surface. Finally, the soft surface may favour a very low rate of running injuries.

Adult↗

PubMed1992

Measurement of isometric force in children with and without Duchenne's muscular dystrophy.

The purpose of this study was to examine the consistency of measurements of maximal isometric force production in children using an electronic strain gauge. A standardized protocol of force testing from the Tufts Quantitative Neuromuscular Examination was adapted to obtain isometric force measurements in seven muscle groups bilaterally. Ten children with Duchenne's muscular dystrophy (DMD) and 10 age-matched children without DMD were recruited for the study. A generalizability framework was used to examine variations in measurements attributable to group differences, test occasions within the same day, and extremity side. Intertester reliability estimates were also completed on a subsample of children with and without DMD. A three-way analysis of variance between groups, sides, and test occasions demonstrated a significant group main effect for all muscle groups. In general, significant main effects were not present for side or test occasion. Test-retest intraclass correlation coefficients (ICCs) for all muscle groups ranged from .88 to .99 for the children with DMD and from .85 to .98 for the children without DMD. Intertester ICCs were slightly lower, ranging from .74 to .97 for the children with DMD and from .71 to .98 for the children without DMD. The results indicate that the electronic strain-gauge protocol produces reproducible force measurements in seven selected muscle groups in children with and without DMD. Brussock CM, Haley SM, Munsat TL, Bernhardt DB. Measurement of isometric force in children with and without Duchenne's muscular dystrophy.

Adolescent↗

PubMed2001

Effects of standard and eccentric overload strength training in young women.

PURPOSE: According to the force-velocity relationship of human skeletal muscle, the maximal load one can lift is limited by the concentric movement phase, and the eccentric phase is always underloaded. In the present study, we hypothesized that acute exercise training using an eccentric overload compared with standard loading would lead to greater neuromuscular and strength adaptations. METHODS: Sedentary women (age 20.9 yr) were tested for concentric and eccentric three-repetition maximum (3RM), maximal isokinetic eccentric and concentric and isometric force and associated EMG activity of selected thigh muscles before and after 7 consecutive days of exercise training of the left quadriceps. The exercise program was designed so that the total weight lifted was similar between the eccentric overload (EO, N = 10) and standard group (ST, N = 10), but EO exercised with about 50% greater eccentric load whereas the controls did not exercise (N = 10). RESULTS: There was a 22% increase in the total weight lifted over 7 d. On the average, EOs compared with STs strength gains were approximately twofold greater. Changes in EMG paralleled the changes in muscle strength without changes in biceps femoris coactivity during knee extension. CONCLUSION: Because the strength gains were achieved by exercising at low intensities and over a short time period, exercise prescription of eccentric overloading appears especially suitable for elders, individuals deconditioned due to an injury, and the chronically diseased.

Adaptation, Physiological↗

PubMed2006

Change of phonation control after cochlear implantation.

OBJECTIVE: To assess the influence of acquired auditory control on some voice parameters in deaf children and adults after cochlear implantation. STUDY DESIGN: Prospective clinical study. SETTING: Tertiary referral center. PATIENTS: Twenty-nine prelingually deafened children and 11 postlingually deafened adults. INTERVENTIONS: The samples of a vowel /a/ were analyzed with an Multi-Dimensional Voice Program (Kay Elemetrics Corporation, Lincoln Park, NJ) before and 6 to 12 months after the cochlear implantation. MAIN OUTCOME MEASURES: The average fundamental frequency (F0), the short-term variation of F0 (JIT) and the amplitude (SH), the very long-term variation of F0 (vF0) and the amplitude (vAm), and the noise-to-harmonic ratio (NHR) were determined and compared for both age groups. The results of the acoustic analysis performed before the implantation were compared with the results after the implantation for children and adults. RESULTS: Significantly greater JIT, SH, vF0, and vAm were detected in the children than in the adults before and after the implantation. The prelingually deafened children significantly improved the control of their phonation after 6 to 12 months' use of the cochlear implant (JIT: p=0.014, SH: p=0.011, vF0: p=0.014, vAm: p=0.031). In the postlingually deafened adults, no significant improvement was found in any of the studied voice parameters after the implantation. F0 showed little or no change after the implantation in children and adults. CONCLUSION: As expected, the voice quality of the prelingually deafened children was significantly worse than that of the postlingually deafened adults. After cochlear implantation, the children significantly improved their short-term and long-term F0 and amplitude variability. In adults, no significant improvement was detected. We suppose that the improvement is a consequence not only of the acquired hearing control but also of the adaptation ability of neuromuscular phonation control and the maturing of these control mechanisms in children. In adults, better phonation quality in general and lesser improvement after the implantation can be the results of well-developed and stable phonation patterns.

Adolescent↗

PubMed2001

The effects of resistance exercise on skeletal muscle abnormalities in patients with advanced heart failure.

Resistance exercise increases muscular strength and endurance, which prevents injuries associated with musculoskeletal disorders, favorably alters muscle fiber type distribution, and up-regulates the genetic expression of certain enzymes seen in dysfunctional skeletal muscles. Although the benefits of resistance exercise are well documented in the literature, this form of exercise is not routinely recommended for patients with heart failure for fear of symptom exacerbation, and because of poor understanding of how best to prescribe this type of exercise. Because muscle atrophy and deconditioning states are common findings in patients with heart failure, these patients stand to benefit substantially from resistance training because this type of physical activity results in functional adaptations in the neuromuscular system. This article addresses changes in skeletal muscle pathophysiology that occur in patients with heart failure and the potential role resistance training may play in reversing this sequela, and recommends a weight lifting exercise prescription for these patients.

Aged↗

PubMed2000

Changes in muscle strength, muscle fibre size and myofibrillar gene expression after immobilization and retraining in humans.

1. Changes in muscle strength, vastus lateralis fibre characteristics and myosin heavy-chain (MyoHC) gene expression were examined in 48 men and women following 3 weeks of knee immobilization and after 12 weeks of retraining with 1866 eccentric, concentric or mixed contractions. 2. Immobilization reduced eccentric, concentric and isometric strength by 47 %. After 2 weeks of spontaneous recovery there still was an average strength deficit of 11 %. With eccentric and mixed compared with concentric retraining the rate of strength recovery was faster and the eccentric and isometric strength gains greater. 3. Immobilization reduced type I, IIa and IIx muscle fibre areas by 13, 10 and 10 %, respectively and after 2 weeks of spontaneous recovery from immobilization these fibres were 5 % smaller than at baseline. Hypertrophy of type I, IIa and IIx fibres relative to baseline was 10, 16 and 16 % after eccentric and 11, 9 and 10 % after mixed training (all P < 0.05), exceeding the 4, 5 and 5 % gains after concentric training. Type IIa and IIx fibre enlargements were greatest after eccentric training. 4. Total RNA/wet muscle weight and ty I, IIa and IIx MyoHC mRNA levels did not change differently after immobilization and retraining. Immobilization downregulated the expression of type I MyoHC mRNA to 0.72-fold of baseline and exercise training upregulated it to 0.95 of baseline. No changes occurred in type IIa MyoHC mRNA. Immobilization and exercise training upregulated type IIx MyoHC mRNA 2.9-fold and 1.2-fold, respectively. For the immobilization segment, type I, IIa and IIx fibre area and type I, IIa and IIx MyoHC mRNA correlated (r = 0.66, r = 0.07 and r = -0.71, respectively). 5. The present data underscore the role muscle lengthening plays in human neuromuscular function and adaptation.

Adult↗

PubMed1987

Patterns of EMG activity of rat plantaris muscle during swimming and other locomotor activities.

The purpose of the study was to examine the patterns of electromyographic (EMG) activity of the rat plantaris during loaded swimming in comparison with other locomotor activities. Five female Sprague-Dawley rats were implanted with chronic bipolar electrodes in the plantaris muscle of the left hindlimb under pentobarbital anesthesia. Characteristics of EMG bursts recorded while the conscious rat was performing treadmill walking (0.24 m/s) were stable and reproducible 10-14 days postsurgery. Following this stabilization period, records of EMG activity were obtained during walking, loaded swimming (6.5 g attached to tail), and several other locomotor tasks. Compared to walking, EMG bursts during loaded swimming were significantly higher (67%) in maximum amplitude, one-third as long in duration, and occurred at a greater rate (4.4 vs. 1.7 bursts/s, P less than 0.05). Swimming bursts were of higher amplitudes than those of all other activities examined and reached 65% of the EMG amplitude recorded following stimulation of the sciatic nerve with supramaximal voltage. The addition of a mass to the animal's tail during swimming did not increase the EMG burst amplitudes but resulted in a higher frequency of bursts. Compared with treadmill walking, loaded swimming elicited burst of high variability in amplitude. Swimming in the rat involves rapid, extensive activation of plantaris, thus providing an exercise model to study the adaptability of the neuromuscular system to prolonged activity of this type.

Animals↗

PubMed1999

Gender differences in the fatigability of human skeletal muscle.

After participating in a 4-wk intervention that reduced normal usage of the elbow flexor muscles, all six women, but only one of six men, experienced a marked increase in the endurance time during a low-force fatiguing contraction. The increase in endurance time was associated with an altered pattern of muscle activation that did not involve the commonly observed progressive increase in muscle activity. Rather, the muscle activity comprised intermittent motor unit activity. In those individuals who exhibited this behavior, the novel pattern of muscle activity was only present immediately after 4 wk of limb immobilization and not before the intervention or after 4 wk of recovery. These findings suggest possible differences between women and men in the adaptations of the neuromuscular system.

Adolescent↗

PubMed1988

Contraction-induced potentiation of human motor unit discharge and surface EMG activity.

In quadrupeds, an electrically induced, moderate to high intensity brief muscle contraction potentiates autogenetic excitation and leads to enhanced recruitment and/or tonic firing frequency of alpha-motor neurons. To determine if similar adaptations occur in humans, single motor units (SMUs) and surface electromyographic activity (EMG) were recorded from the right biceps brachii before and immediately after a 5-s 25% or 50% maximum voluntary contraction (MVC), while subjects held a handle (0-1% MVC) attached to a force transducer or maintained a 2% MVC for 30-60 s. Of 26 SMUs recorded, 15 increased, 4 decreased, and 7 showed no change in firing frequency (mean increase: 5 imp/s, P less than 0.01). Twelve SMUs had lower recruitment force thresholds after contraction. There was no significant treatment effect for the % MVC intensity. The postcontraction surface EMG power spectrum broadened, increased in amplitude, and contained a higher frequency component than the control contraction power spectrum. Changes in recruitment and/or frequency coding were reflected in the raw EMG records. Findings agree with previous reports in animals of contraction-induced potentiation of subsequent submaximal muscle contractions. Such acute adaptations in spinal neuromuscular pathways would function to optimize force output to a submaximal range of neural input frequencies.

Electromyography↗

PubMed1992

Changes in mandibular masticatory movements after insertion of nonworking-side interference.

To investigate the influence of nonworking-side interferences on mandibular masticatory movements and signs and symptoms of dysfunction of the masticatory system, an experimental balancing-side interference was introduced in 12 healthy subjects for 1 week. The individual response to the interference varied substantially. However, some of the movement variables were significantly changed immediately after insertion, but an adaptation of the neuromuscular system to the interference was evident at the end of the experimental period.

Adult↗

PubMed1991

Isolated dislocation of the radial head.

Fifty-four patients (12 bilateral) with isolated dislocations of the radial head were encountered over a 20-year period. The congenital varieties (26 patients) included isolated unilateral, familial, synostosis-related, and syndrome-related. The acquired types (28 patients) involved trauma, neuromuscular impairment, or adaptive dislodgments. Acute, traumatic dislocation (17 patients) was the most common presentation. Others were diagnosed incidentally, or associated with discomfort, dysfunction, or deformity. Closed reduction of an acute traumatic dislocation was generally successful (16 of 17 patients). Realignment attempts (three cases) on late diagnosed traumatic cases and isolated congenital types were invariably unsuccessful, eventually requiring radial head excision. Four patients underwent excision of the head of the radius as primary treatment.

Adolescent↗

PubMed1982

Effect of castration on the morphology of the motor end-plates of the rat levator ani muscle.

The levator ani (L. A.) muscle, part of the genital apparatus of rodents, atrophies after castration. Changes in end-plate structure in the L. A. muscle of castrated male rats were examined with correlated light and electron microscopic methods. Four months after castration acetylcholinesterase staining reveals, in some muscle fibres, the presence of subneural gutters composed of a succession of cuplets whereas the subneural gutters are continuous and ramified in control muscles. Six months after castration most of the end-plates are further modified. Their terminal arborization, as revealed by silver nitrate staining, is more tortuous and irregular than in controls. At the ultrastructural level, reduced sole-plate and superimposed axonal endings are seen in some end-plates three months after castration. Our findings demonstrate that the changes (reduction of muscular activity and atrophy of muscle) are accompanied by adaptations of the neuromuscular junctions. As receptors for testosterone are known to be present in these motoneurons and muscle fibres, the observed morphological changes might be under the control of testosterone acting on both muscle and motoneurons.

Acetylcholinesterase↗

PubMed2004

Neuromuscular characteristics of endurance- and power-trained athletes.

In response to chronic physical training, the human neuromuscular system undergoes significant and specific adaptations. More importantly, these influences are the result of the type and quantity of physical activity. One of the simplest neuromuscular mechanisms is the spinal stretch reflex. The reflex system was previously viewed as inflexible, with a relatively fixed response that could vary only slightly. However, more recent data have identified an adaptive plasticity in the reflex system. In this respect, the reflex system can be used to assess training and aging adaptations of the human neuromuscular system. Due to their methodological simplicity, both the tendon-tap reflex and the electrically evoked Hoffmann reflex (H-reflex) can be used to assess training adaptations of the human neuromuscular system. The purpose of this paper is to review briefly the tendon-tap and H-reflex paradigms and delineate the research findings pertaining to changes in the reflex system with physical training. For purposes of clarity, this discussion will be divided into the following: (a) differences observed in the tendon-tap reflex, (b) differences observed in the H-reflex, and (c) role of interneurons in mediating these changes.

Humans↗

PubMed2002

Effects of electrical stimulation-induced leg training on skeletal muscle adaptability in spinal cord injury.

Neuromuscular electrical stimulation has grown in popularity as a therapeutic device for training and an ambulation aid to human paralyzed muscle. Despite its current clinical use, few studies have attempted to concurrently investigate the functional and intramuscular adaptations which occur after electrical stimulation training. Six individuals with a spinal cord injury performed 10 weeks of electrical stimulation leg cycle training (30 min d(-1), 3 d week(-1)). The paralyzed vastus lateralis muscle showed significant alterations in skeletal muscle characteristics after the training, indicated by an improvement in total work output (52-112 kJ; P < 0.05), an increase in fiber cross-sectional area (18 to 41 x 10(2) microm(2); P < 0.05), a reduction in the percentage of type IIX fibers (75% to 12%; P < 0.05), a decrease in myosin heavy chain IIx (68% to 44%; P < 0.05), an increase in capillary density (2-3.5 capillaries around fiber; P < 0.05) and increases in activity levels of citrate synthase (7-16 mU mg(-1) protein) and hexokinase (1.2-2.4 mU mg(-1) protein). This study showed that 10 weeks of electrical stimulation training of human paralyzed muscle induces concurrent improvements in functional capacity and oxidative metabolism.

Adaptation, Physiological↗

PubMed2002

Motoneuron and sensory neuron plasticity to varying neuromuscular activity levels.

The size and phenotypic properties of the neural and muscular elements of the neuromuscular unit are matched under normal conditions. When subjected to chronic decreases or increases in neuromuscular activity, however, the adaptations in these properties are much more limited in the neural compared with the muscular elements.

Adaptation, Physiological↗

PubMed1984

Morphologic response to changes in neuromuscular patterns experimentally induced by altered modes of respiration.

The present experiment was designed to test whether specific recordable changes in the neuromuscular system could be associated with specific alterations in soft- and hard-tissue morphology in the craniofacial region. The effect of experimentally induced neuromuscular changes on the craniofacial skeleton and dentition of eight rhesus monkeys was studied. The neuromuscular changes were triggered by complete nasal airway obstruction and the need for an oral airway. Alterations were also triggered 2 years later by removal of the obstruction and the return to nasal breathing. Changes in neuromuscular recruitment patterns resulted in changed function and posture of the mandible, tongue, and upper lip. There was considerable variation among the animals. Statistically significant morphologic effects of the induced changes were documented in several of the measured variables after the 2-year experimental period. The anterior face height increased more in the experimental animals than in the control animals; the occlusal and mandibular plane angles measured to the sella-nasion line increased; and anterior crossbites and malposition of teeth occurred. During the postexperimental period some of these changes were reversed. Alterations in soft-tissue morphology were also observed during both experimental periods. There was considerable variation in morphologic response among the animals. It was concluded that the marked individual variations in skeletal morphology and dentition resulting from the procedures were due to the variation in nature and degree of neuromuscular and soft-tissue adaptations in response to the altered function. The recorded neuromuscular recruitment patterns could not be directly related to specific changes in morphology.

Animals↗

PubMed2004

The mouse as a model of cardiovascular adaptations to microgravity.

There are a multitude of physiological adaptations to microgravity, involving the cardiovascular, neuromuscular, and neuroendocrine systems. Some of these adaptations lead to cardiovascular deconditioning on return to normal gravity, posing a threat to human functional integrity after long-term spaceflight. Animal models of microgravity, e.g., tail suspension in rats, have yielded important information regarding the mechanism of these adaptations and have been useful in the design of countermeasures. The mouse could potentially be a useful experimental model, given its small size (smaller and lighter payload) and the powerful tools of experimental mouse genetics, which allow us to dissect mechanisms on a gene-specific basis. We show that the mouse demonstrates a wide range of cardiovascular responses to simulated microgravity, including alterations in heart rate, exercise capacity, peripheral arterial vasodilatory responsiveness, and baroreflex response. These responses are qualitatively similar to many of those demonstrated in humans during spaceflight and in rats using tail suspension, although there are some important differences. Thus the mouse has value as a model for studies of cardiovascular changes during microgravity; however, investigators must maintain an appreciation of important species differences.

Adaptation, Physiological↗